1. Field of the Invention
The present invention relates to the formation of a material layer by chemical vapor deposition (CVD) and, in particular, to a method and apparatus for the non-contact, in-situ measurement of the temperature of a diamond film, or other film material, during its chemical vapor deposition on an underlying substrate.
2. Description of the Related Art
It has long been known that diamond can be used in many diverse applications. In particular, diamond is finding increased use in the electronics industry.
Given the relative scarcity of natural diamond, there has been for some time a concerted effort to synthesize diamond in the laboratory. More recently, it has been found that it is possible to commercially produce polycrystalline diamond film using chemical vapor deposition (CVD) techniques.
Chemical vapor deposition, as its name implies, involves a gas-phase chemical reaction occurring above the surface of a solid substrate, which caused deposition of a CVD material film onto the substrate surface.
All CVD techniques for producing diamond films require some means of activating gas-phase carbon-containing precursor molecules. This generally involves thermal or plasma activation, or the use of a combustion flame. While each technique may differ in its details, they all share common features. For example, CVD growth of diamond normally requires that the substrate on which the diamond film is grown be maintained at a predefined temperature during the CVD process.
One of the problems associated with manufacture of CVD diamond is that the higher growth rates required for commercial feasibility are achieved only with a corresponding decrease in diamond film quality. To a great extent, this loss of quality results from a lack of precise temperature control of the deposited material during the CVD process.
Therefore, it would be highly desirable to have available a technique for measuring and, thus, for controlling the temperature of deposited diamond film during the CVD process.
The present invention provides a method and apparatus for the non-contact, in-situ temperature measurement of a layer of material during chemical vapor deposition (CVD) of the layer of material. In accordance with the invention, magnitude modulated ultraviolet (UV) light having a plurality of separated spectral components is directed at the deposited material. The modulated UV light has a plurality of wavelengths corresponding to different temperature dependencies of absorptance in the deposited material. The separated spectral components are within transparency spectral windows of a plasma media contained in the CVD reactor. A portion of the magnitude modulated UV light is directed as a reference into a comparison device, such as a spectrophotometer. The light reflected by the deposited material is also directed from the CVD reactor into the comparison device. That is, the magnitudes of the magnitude modulated component of reflected light and the reference light are compared at more than one spectral component. From this comparison is derived the temperature of the deposited material. The results of the comparison are then utilized in a feedback loop to control the temperature of the deposited material, typically by controlling the temperature of the substrate on which the material is being deposited.
Those skilled in the art will appreciate that the techniques of the present invention can be used for materials other than diamond by adjusting the spectral windows of light in the algorithm for deriving the deposited film temperature based on results of the magnitude comparisons for that particular material and CVD conditions.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description and accompanying drawings that set forth an illustrative embodiment in which the principles of the invention are utilized.